iOS 8 will be available as an over-the-air update for the iPhone 4S and later, iPad 2 and later, iPad Mini, and the fifth-generation iPod Touch. Alternately, users can download the upgrade through iTunes on a Mac or Windows PC, then apply it to an iPhone, iPad or iPod Touch connected to the computer.

Customers should expect glitches in the download process: There are invariably complaints lodged on Apple's support forums by users who report failed downloads of a just-released iOS. The usual assumption is that servers are swamped.

But that won't stop the griping, or Apple repeating the year-in-year-out problems.

"You'd think the geniuses at Apple would innovate mass software distribution since this happens EVERY YEAR," said an iPhone owner identified as "bradwest414" in September 2013 about iOS 7 download troubles.

Expect to see that -- or even experience it -- tomorrow as well.

But Apple's ability to push iOS 8 to users Wednesday will be scrutinized more carefully than usual: The Cupertino, Calif. company has stumbled twice in the past week with online events. On Tuesday, Sept. 9, the live webcast of the iPhone introduction was a disaster. During the first third to half of the one hour 45-min. broadcast, people faced repeated interruptions and black screens, saw "Access Denied" error messages, and heard a Chinese translator talking over CEO Tim Cook.

Days later, when Apple opened pre-orders for the iPhone 6 and iPhone 6 Plus, the online store opened late. Once it appeared, it was often inaccessible.

To prepare a device for an iOS upgrade, Apple recommends that users back up the iPhone's, iPad's or iPod Touch's content to iCloud or iTunes. Instructions for the backup process can be found on Apple's support site.

Tomorrow, users can initiate a manual download and upgrade by tapping the "Settings" icon, then the "General" button on the ensuing screen. Touching "Software Update" will kick off the task.

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